1. Field of the Invention
The present invention relates to a punch press for punching a plate workpiece, and more specifically to a punch press provided with an automatic tool exchange device for exchanging the tool set of a punch and die arranged at the process position with another tool set.
2. Description of the Prior Art
In general, a punch press is constructed having a C-shpaed frame structure such that an upper frame is supported by a column standing on one side of a base in cantilever fashion. A die is fitted to a die holder disposed on the base, and a punch is attached to the lower part of a ram or a punch holder supported by the upper frame so as to the movable up and down in order to punch a plate workpiece in cooperation with the die.
In the conventional punch press, usually a ram drive unit for driving the ram (which moves the punch holder up and down) is mounted on one end of the upper frame. In this case, a clutch-brake unit is mounted at one end of the upper frame or a clutch unit and a brake unit are mounted separately on both the right and left sides of the upper frame when seen from the front of the press. Therefore, there exist problems such that the influence of heat generated from the ram drive unit is different between the right and left sides of the upper frame so that the upper frame is subjected to deformation. In addition, it has been difficult to mount the drive unit on the upper frame located at a high position.
Further, in the conventional punch press, when various punching processings are effected with a single tool set by pivoting the punch and die together in various directions, since the punch holder is moved up and down and further pivoted, when the press is operated for many hours, there exists a problem in that a clearance increases between the punch holder and the pivotal member and therefore the punch holder section tends to slip in the circumferential direction thereof, thus deteriorating the processing precision.
Further, the conventional punch press is provided with an automatic tool exchange device for automatically exchanging a tool set of punch and die fitted to the punch holder and the die holder at the process position with another tool set, so that various punching processings of different shapes can be made for the same workpiece.
In the punch press provided with the automatic tool exchange device, a die fixing device for automatically fixing a die to the die holder is provided. This die fixing device includes a die push member for urging and fixing the die to the die holder. A known die fixing device is such that a die is urged toward the die holder by shifting a pivotal die push member from a horizontal position to a vertical position. In the prior-art die fixing device as described above, however, since the stroke of the die push member is long, there exists a problem in that a device for operating the die push member is bulky and therefore the whole punch press inevitably increases in dimensions.
Furthermore, in the prior-art punch press provided with the automatic tool exchange device, a stopper is provided to determine stop positions of the arms of the tool exchange device. However, in the case where the arms are located at three different angular positions, there exists a problem such that the intermediate stop position is offset by a distance corresponding to the stopper thickness when the arm is brought into contact with the stopper.